NONMEM Users Network Archive

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Re: Simulation problem of normal distributed data

From: Navin Goyal <navingoyal>
Date: Tue, 29 Jul 2014 18:25:05 -0400

Hi Sheng,
I don't know the exact reason behind such mysterious behavior but if you
just change the seed number (the UNIFORM seed) it works.
 e.g. I changed the seed# from 7545 to 17545 and was able to simulate
1000 rows for the subject.

$SIMULATION (6446) (*1*7545 UNIFORM) ONLYSIM NOPRED SUB=1

Its a rare occurrence but may be the seed number caused some issue (while
generating sufficient samples to satisfy the constraints you set up using
the DOWHILE LOOP). For example I think the same seed number (7545) may work
when the DOWHILE condition is reversed
(RL .*LT*. PRN) however it may not be appropriate based on your
problem. .......or
may be there is some other explanation to such occurrence.

Kind regards
Navin Goyal






On Tue, Jul 29, 2014 at 10:54 AM, Gerry Sheng <shengyc

> Dear NMuser,
>
> I encountered a strange problem when I used the following code to simulate
> normal distributed data. When the data records >797, no result appears with
> NONMEM run into an infinite loop . But when the records decreasing to 796
> (delete the last row), the results will occurred immediately. Anyone else
> met this phenomenon? Any comments and suggestions are appreciated. Thank
> you in advance.
>
> $PROBLEM PD
> $INPUT ID,CONC,DV
> $DATA data.csv IGNORE=
>
> $PRED
> NMEAN=THETA(1)+ETA(1)
> SD=THETA(2)
>
> ;Simulate count
> IF (ICALL.EQ.4) THEN
> N=0
> PRN=0
> CALL RANDOM(2, R)
> RL=1-R
> DO WHILE (RL .GT. PRN)
> LNNOR=LOG(6.283185)+2*LOG(SD)+((N-NMEAN)/SD)**2
> PY=EXP(-0.5*LNNOR)
> PRN=PRN+PY
> IF (PRN .LT. RL) N=N+1
> ENDDO
> DV=N
> ENDIF
>
> $THETA
> (30,41.7,60) ;MEAN
> (2,14.4,50) ;SD
>
> $OMEGA
> 0 FIX ;MEAN
>
> $SIMULATION (6446) (7545 UNIFORM) ONLYSIM NOPRED SUB=1
> $TABLE ID TIME DV ONEHEADER NOPRINT FILE=npctab1.dta
>
> data.csv like this
> ID CONC DV
> 1 0 .
> 1 0 .
> 1 0 .
> 1 0 .
> 1 0 .
> 1 0.01 .
> 1 0.01 .
> 1 0.01 .
> 1 0.01 .
> 1 0.01 .
> .....
>
> Yucheng Sheng
>
> Research Associate
> School of Pharmacy, UCL
>



--
Navin Goyal

Received on Tue Jul 29 2014 - 18:25:05 EDT

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